a HUGE improvement in tone. clear as a bell, still has all the growl but has a fatter low end. i HIGHLY recommend this mod to anyone who has a 9v warwick. the preamp works fine at 18v as well. (so far ) all you have to do is get a 9v battery clip from radio shack, cut the black wire from the existing battery clip in half, and stick the new battery holder in between the two halves, with the red side of the new battery holder going towards the old battery clip. you have to remove the plastic battery storage area to get both batteries to fit in there, but if you use some foam the batteries wont knock around.